grafana/k6 · error

unexpected error while getting the summary wrapper: %w

Error message

unexpected error while getting the summary wrapper: %w

What it means

An internal error occurred while evaluating the handleSummary wrapper code that k6 builds by splicing the jslib summary implementation into a wrapper lambda. This is not caused by user summary logic itself failing — it fires when the generated wrapper cannot even be compiled/run by the Sobek runtime, indicating an internal k6 bug or corrupted embedded jslib bundle rather than a script mistake.

Source

Thrown at internal/js/runner.go:407

		r, vu.Runtime, legacy, s, meta,
	)
	if err != nil {
		return nil, err
	}

	callbackResult, err := runUserProvidedHandleSummaryCallback(summaryCtx, vu, handleSummaryData)
	if err != nil {
		return nil, err
	}

	if deadlineError := r.checkDeadline(summaryCtx, consts.HandleSummaryFn, nil, nil); deadlineError != nil {
		return nil, deadlineError
	}

	wrapper := strings.Replace(summaryWrapperLambdaCode, "/*JSLIB_SUMMARY_CODE*/", summaryCode, 1)
	handleSummaryWrapperRaw, err := vu.Runtime.RunString(wrapper)
	if err != nil {
		return nil, fmt.Errorf("unexpected error while getting the summary wrapper: %w", err)
	}
	handleSummaryWrapper, ok := sobek.AssertFunction(handleSummaryWrapperRaw)
	if !ok {
		return nil, fmt.Errorf("unexpected error did not get a callable summary wrapper")
	}

	wrapperArgs := prepareHandleWrapperArgs(
		vu, noColor, enableColors, newMachineReadableSummary, callbackResult, handleSummaryData, summaryData,
	)
	rawResult, _, _, err := vu.runFn(summaryCtx, false, handleSummaryWrapper, nil, wrapperArgs...)

	if deadlineError := r.checkDeadline(summaryCtx, consts.HandleSummaryFn, rawResult, err); deadlineError != nil {
		return nil, deadlineError
	}

	if err != nil {
		return nil, fmt.Errorf("unexpected error while generating the summary: %w", err)
	}

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Upgrade to the latest k6 release; the embedded jslib summary bundle may be fixed
2. Report the issue to the k6 GitHub repository with the script and k6 version
3. As a workaround, avoid exporting a custom handleSummary so the default summary path is used

When it happens

Trigger: Thrown at internal/js/runner.go:407 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/07d77cebd48825e8. Report an issue: GitHub.